WEBVTT 00:00:00.500 --> 00:00:03.975 Welcome to GCSE Edexcel Science revision. 00:00:04.125 --> 00:00:08.345 Unit C B 5: Health, disease and the development of medicines. 00:00:11.000 --> 00:00:16.223 Health includes physical, mental and social well-being, not only the absence of disease. 00:00:16.373 --> 00:00:19.007 Problems in one area can affect the others. 00:00:21.667 --> 00:00:26.529 Communicable diseases are caused by pathogens and can spread between organisms. 00:00:26.679 --> 00:00:31.552 Non-communicable diseases are not passed from one person to another by infection. 00:00:34.233 --> 00:00:39.936 A pathogen is a disease-causing agent, such as a bacterium, virus, fungus or protist. 00:00:40.086 --> 00:00:42.710 Not all microorganisms cause disease. 00:00:45.367 --> 00:00:48.362 One disease can increase vulnerability to another. 00:00:48.512 --> 00:00:54.677 For example, H I V damages immune defences, so other infections can become harder to control. 00:00:57.333 --> 00:01:00.350 A correlation is a pattern linking two variables. 00:01:00.500 --> 00:01:03.697 It does not prove that one causes the other (causation). 00:01:03.847 --> 00:01:10.837 For example, income and life expectancy may be linked, but healthcare, nutrition and housing can also affect the pattern. 00:01:13.500 --> 00:01:17.750 Compare health data using suitable samples, rates or percentages. 00:01:17.900 --> 00:01:22.136 Look for other factors that could explain the pattern (confounding factors). 00:01:22.286 --> 00:01:26.407 An increased risk means something is more likely, not certain to happen. 00:01:29.067 --> 00:01:35.817 Many non-communicable diseases result from interacting genetic, environmental and lifestyle factors. 00:01:35.967 --> 00:01:41.469 Examples include cardiovascular disease, some cancers and some lung or liver diseases. 00:01:44.133 --> 00:01:50.585 Malnutrition means an unbalanced intake of nutrients or energy, including deficiencies and excesses. 00:01:50.735 --> 00:01:56.590 Lack of vitamin C can cause scurvy; excess energy intake can contribute to increased body fat. 00:01:59.267 --> 00:02:02.706 Diet and physical activity affect energy balance. 00:02:02.856 --> 00:02:11.707 Long-term energy intake exceeding energy expenditure can contribute to obesity, which is associated with increased risk of several diseases. 00:02:14.367 --> 00:02:20.297 Body mass index (B M I) equals mass in kilograms divided by (height in metres)squared. 00:02:20.447 --> 00:02:25.054 Square the height before dividing; convert centimetres to metres if needed. 00:02:27.733 --> 00:02:37.726 A hypothetical adult of mass seventy two kilograms and height one point eight metres has body mass index equal to seventy two divided by one point eight squared, 00:02:37.876 --> 00:02:41.235 which equals twenty two point two to one decimal place. 00:02:43.900 --> 00:02:52.197 In the conventional adult B M I classification commonly used in GCSE examples, 30 or above indicates obesity. 00:02:52.347 --> 00:03:01.242 B M I is a screening measure, not a diagnosis; it cannot distinguish muscle from fat, and children require age-related interpretation. 00:03:03.900 --> 00:03:08.652 Waist : hip ratio equals waist circumference divided by hip circumference. 00:03:08.802 --> 00:03:16.333 Use the same units: a waist of 80 centimetres and hips of 100 centimetres give a ratio of 0.80. 00:03:19.000 --> 00:03:25.880 B M I and waist : hip ratio can contribute to risk assessment, but do not capture every influence on health. 00:03:26.030 --> 00:03:32.162 Use the information supplied in an exam question rather than diagnosing an individual from one value. 00:03:34.833 --> 00:03:41.574 Alcohol misuse can damage the liver and contribute to cirrhosis, where healthy tissue is replaced by scar tissue. 00:03:41.724 --> 00:03:45.199 Alcohol is not the only possible cause of liver disease. 00:03:47.867 --> 00:03:54.905 Smoking increases cardiovascular risk by damaging blood vessels and contributing to plaque formation and clotting. 00:03:55.055 --> 00:04:01.827 Nicotine can raise heart rate and blood pressure; carbon monoxide reduces the blood’s oxygen-carrying capacity. 00:04:04.500 --> 00:04:10.814 Lifestyle-related disease affects individuals and families, healthcare services and wider society. 00:04:10.964 --> 00:04:18.941 Population effects depend on exposure, access to care and other factors; avoid assuming that a disease is solely a person’s fault. 00:04:21.600 --> 00:04:25.181 Cardiovascular disease affects the heart or blood vessels. 00:04:25.331 --> 00:04:31.112 In coronary heart disease, fatty deposits can narrow the coronary arteries supplying heart muscle. 00:04:33.767 --> 00:04:39.513 Reduced blood flow limits the supply of oxygen for aerobic respiration in heart muscle. 00:04:39.663 --> 00:04:43.169 A clot blocking a coronary artery can cause a heart attack. 00:04:45.833 --> 00:04:49.288 Lifestyle changes can reduce cardiovascular risk. 00:04:49.438 --> 00:04:55.655 Their benefits usually develop over time; they do not instantly remove an established arterial blockage. 00:04:58.333 --> 00:05:02.727 Medicines such as statins lower blood cholesterol and can reduce risk. 00:05:02.877 --> 00:05:08.433 They may require long-term use and can have side effects, so evaluate benefits and limitations. 00:05:11.100 --> 00:05:16.305 A stent is a small mesh tube inserted into a narrowed artery to help keep it open. 00:05:16.455 --> 00:05:20.671 Angioplasty widens the artery, and the stent supports the opening. 00:05:20.821 --> 00:05:26.227 A stent supports a widened passage; it does not remove every underlying risk factor. 00:05:30.900 --> 00:05:40.306 Coronary bypass surgery uses a blood vessel graft to make an alternative route around a narrowed or blocked artery, improving blood supply to heart muscle. 00:05:42.967 --> 00:05:51.509 Stents and bypass surgery can improve blood flow relatively quickly, but involve procedural risks and do not remove all underlying risk factors. 00:05:54.167 --> 00:06:00.389 Compare treatments using effectiveness, side effects, surgical risk, recovery, long-term care and cost. 00:06:00.539 --> 00:06:04.507 The most suitable treatment depends on the condition and the person. 00:06:07.167 --> 00:06:10.823 Bacteria are cells that can reproduce in suitable conditions. 00:06:10.973 --> 00:06:18.546 Some cause disease by damaging tissues or producing toxins; viruses reproduce inside host cells and can damage them. 00:06:21.200 --> 00:06:25.127 Cholera is caused by bacteria and can cause severe diarrhoea. 00:06:25.277 --> 00:06:29.575 It is commonly spread by water contaminated with infected faeces. 00:06:32.233 --> 00:06:36.802 Tuberculosis (TB) is caused by bacteria and can damage the lungs. 00:06:36.952 --> 00:06:41.825 Infectious material from a person with respiratory TB can spread through the air. 00:06:44.500 --> 00:06:49.183 Chalara ash dieback is caused by a fungus, Hymenoscyphus fraxineus. 00:06:49.333 --> 00:06:55.059 It causes leaf loss and bark lesions in ash trees; airborne fungal spores can spread infection. 00:06:57.733 --> 00:07:03.013 Athlete’s foot is a fungal infection that affects human skin, especially between the toes. 00:07:05.667 --> 00:07:10.403 Malaria is caused by Plasmodium protists and can damage blood and the liver. 00:07:10.553 --> 00:07:14.314 Mosquitoes act as vectors that carry the pathogen between people. 00:07:16.967 --> 00:07:20.601 H I V is a virus that damages immune-system cells. 00:07:20.751 --> 00:07:29.454 Untreated infection can lead to AIDS, leaving the body much less able to control other infections; effective treatment can prevent this progression. 00:07:32.133 --> 00:07:36.667 Chlamydia is a bacterial sexually transmitted infection (S T I). 00:07:36.817 --> 00:07:43.536 H I V can also be sexually transmitted, but it is caused by a virus, so the two pathogens are different types. 00:07:46.200 --> 00:07:49.069 A vector transports a pathogen between hosts. 00:07:49.219 --> 00:07:56.263 In malaria, the mosquito is the vector and the Plasmodium protist is the pathogen; they are not the same organism. 00:07:58.933 --> 00:08:06.239 Clean water supplies, sewage treatment and hygiene reduce faecal contamination and help prevent cholera transmission. 00:08:06.389 --> 00:08:10.321 Handwashing also reduces transfer of some pathogens to the mouth. 00:08:13.000 --> 00:08:20.786 Ventilation and appropriate infection-control measures reduce airborne transmission, including the spread of respiratory TB. 00:08:20.936 --> 00:08:23.964 Different transmission routes require different controls. 00:08:26.633 --> 00:08:36.381 For malaria, insecticide-treated mosquito nets, reducing breeding sites and controlling mosquitoes can reduce contact with the vector and interrupt transmission. 00:08:39.033 --> 00:08:45.933 Control measures for ash dieback aim to limit movement of infected material and follow plant-health guidance. 00:08:46.083 --> 00:08:49.218 Airborne spores make complete prevention difficult. 00:08:51.900 --> 00:08:59.386 S T I s such as chlamydia and H I V can spread through sexual contact involving infected fluids or tissues. 00:08:59.536 --> 00:09:05.381 Condoms reduce the risk of transmission; they do not guarantee protection against every S T I. 00:09:08.033 --> 00:09:12.939 Screening can identify infections, including those without obvious symptoms. 00:09:13.089 --> 00:09:20.810 Detection enables treatment and measures to reduce onward transmission; avoiding sexual contact prevents exposure by that route. 00:09:23.467 --> 00:09:27.205 Skin is a physical barrier that reduces entry of pathogens. 00:09:27.355 --> 00:09:30.095 Breaks in the skin can provide an entry route. 00:09:32.767 --> 00:09:35.877 Mucus traps particles and pathogens in the airways. 00:09:36.027 --> 00:09:40.306 Cilia move the mucus towards the throat, helping clear trapped material. 00:09:42.967 --> 00:09:48.023 Tears contain lysozyme, an enzyme that breaks down cell walls of some bacteria. 00:09:48.173 --> 00:09:51.547 This is a chemical defence, rather than a physical wall. 00:09:54.200 --> 00:10:00.727 Hydrochloric acid in the stomach creates acidic conditions that help destroy many swallowed pathogens. 00:10:00.877 --> 00:10:02.840 It is a chemical defence. 00:10:02.990 --> 00:10:07.118 Physical barriers and clearance work alongside chemical defences. 00:10:11.800 --> 00:10:18.125 Physical barriers reduce entry or remove pathogens; chemical defences use substances that damage them. 00:10:18.275 --> 00:10:22.207 These general defences do not target one particular antigen. 00:10:24.867 --> 00:10:31.074 Antigens are molecules, often on a pathogen’s surface, that can trigger a specific immune response. 00:10:31.224 --> 00:10:33.741 Different pathogens have different antigens. 00:10:36.400 --> 00:10:40.748 Lymphocytes are white blood cells involved in specific immune responses. 00:10:40.898 --> 00:10:49.526 Those that recognise a particular antigen multiply and produce antibodies with binding sites that match (are complementary to) that antigen. 00:10:52.200 --> 00:10:56.228 Antibodies are proteins that bind specifically to matching antigens. 00:10:56.378 --> 00:11:05.326 They can neutralise pathogens or toxins and help other immune cells remove pathogens; binding does not mean every pathogen is instantly destroyed. 00:11:08.000 --> 00:11:13.013 Other white blood cells, including phagocytes, can engulf and digest pathogens. 00:11:13.163 --> 00:11:16.064 Antibodies can help mark a pathogen for removal. 00:11:18.733 --> 00:11:22.326 The first exposure produces a primary immune response. 00:11:22.476 --> 00:11:27.095 There is a delay while the appropriate lymphocytes are activated and multiply. 00:11:29.767 --> 00:11:34.385 Some lymphocytes become memory cells and remain after the initial response. 00:11:34.535 --> 00:11:39.027 They enable a faster response if the same antigen is encountered again. 00:11:41.700 --> 00:11:47.437 The secondary response usually produces antibodies more rapidly and in greater quantities. 00:11:47.587 --> 00:11:53.889 Specificity means memory for one antigen does not automatically protect against every other pathogen. 00:11:56.567 --> 00:12:03.465 Vaccination introduces a safe form of an antigen, for example from an inactive pathogen or a harmless part of it. 00:12:03.615 --> 00:12:08.745 This stimulates an immune response without causing the disease the vaccine aims to prevent. 00:12:11.400 --> 00:12:15.727 The immune system produces specific antibodies and memory lymphocytes. 00:12:15.877 --> 00:12:22.468 Vaccination prepares the body for a later encounter; it does not simply supply a permanent stock of antibodies. 00:12:25.133 --> 00:12:31.095 On later exposure to the matching pathogen, memory cells enable a faster secondary response. 00:12:31.245 --> 00:12:34.765 The pathogen may be controlled before serious symptoms develop. 00:12:37.433 --> 00:12:41.397 Vaccine protection varies between pathogens, vaccines and people. 00:12:41.547 --> 00:12:46.001 Some vaccines require additional doses to build or maintain protection. 00:12:48.667 --> 00:12:58.383 A graph of antibody level against time can compare responses: the secondary response rises sooner and often reaches a higher level than the primary response. 00:12:58.533 --> 00:13:01.282 Interpret the axes and exposure times. 00:13:01.432 --> 00:13:05.839 Responses to the same antigen: schematic trend, not measured data. 00:13:10.500 --> 00:13:16.749 Antibiotics treat bacterial infections by killing bacteria or stopping their growth (inhibiting it). 00:13:16.899 --> 00:13:23.244 They target bacterial processes, such as making cell walls, that differ from processes in human cells. 00:13:25.900 --> 00:13:28.811 Antibiotics do not treat viral infections. 00:13:28.961 --> 00:13:35.637 Viruses use host-cell machinery and lack the bacterial structures or processes targeted by these medicines. 00:13:38.300 --> 00:13:43.739 Antibiotic-resistant bacteria survive a treatment that kills susceptible bacteria. 00:13:43.889 --> 00:13:48.094 Selection can make resistance more common as the survivors reproduce. 00:13:50.767 --> 00:13:55.438 Appropriate antibiotic use reduces unnecessary selection pressure. 00:13:55.588 --> 00:14:00.921 Pain-relieving medicines can relieve symptoms, but this does not mean they remove the pathogen. 00:14:03.600 --> 00:14:08.442 Medicine development starts by finding a substance that might have a useful effect. 00:14:08.592 --> 00:14:15.395 Researchers develop it into a form that can be given to a patient (a formulation) and investigate how it works. 00:14:18.067 --> 00:14:26.081 Before testing on humans, preclinical studies test a possible medicine on cells or tissues and, where appropriate, whole organisms. 00:14:26.231 --> 00:14:32.545 Researchers check its effects and toxicity (how harmful it is) and find out how it behaves in the body. 00:14:35.200 --> 00:14:42.527 Early clinical trials often use small numbers of healthy volunteers to study safety, side effects and suitable doses. 00:14:42.677 --> 00:14:47.950 Some medicines, such as certain cancer treatments, are first tested in patients instead. 00:14:50.600 --> 00:14:56.497 Later clinical trials include people with the condition and assess efficacy: how well the treatment works. 00:14:56.647 --> 00:15:02.906 Larger trials also give more information about side effects and comparisons with existing treatments. 00:15:03.056 --> 00:15:08.251 Studies move from preclinical tests to human trials, followed by review and monitoring. 00:15:12.933 --> 00:15:16.876 Random allocation helps make treatment and comparison groups similar. 00:15:17.026 --> 00:15:23.809 A placebo is a treatment without the tested active ingredient; some trials instead compare with an existing medicine. 00:15:26.467 --> 00:15:34.294 In a double-blind trial, participants and the relevant researchers assessing outcomes do not know which treatment each person receives. 00:15:34.444 --> 00:15:37.557 This helps reduce expectation and observer bias. 00:15:40.233 --> 00:15:44.491 Trials require informed consent, ethical review and monitoring. 00:15:44.641 --> 00:15:49.665 A placebo is not suitable if it would mean withholding essential effective treatment. 00:15:52.333 --> 00:15:58.067 Evaluate a medicine using efficacy, safety, appropriate dose and the quality of the evidence. 00:15:58.217 --> 00:16:04.254 A larger trial can detect effects missed by a small trial, but cannot prove a medicine has no risks. 00:16:06.933 --> 00:16:12.138 After approval, continued monitoring can identify rare or long-term side effects. 00:16:12.288 --> 00:16:16.983 Passing early tests is not a guarantee that every later study will be successful. 00:16:19.633 --> 00:16:23.011 That completes Health, disease and the development of medicines. 00:16:23.161 --> 00:16:26.507 Revisit the notes and test yourself on the revision website.